On Mon, May 09, 2016 at 04:41:31PM -0700, Dave Hansen wrote: > On 05/09/2016 01:46 PM, Yu-cheng Yu wrote: > > When XSAVES is used, xsave.header.xcomp_bv[63] must be set. > > So, that's not strictly correct. XSAVES can write to a completely empty > (0'd) memory buffer. It's only XRSTORS that _needs_ bit 63 set. The > instruction reference is pretty clear on this point.
You mean the comments? I will change it to XRSTORS. > > Oh, and if you decided to do this for some reason, please have mercy and > go make a macro for 1<<63. > > Also, I don't think the kernel ever checks for this bit. So are we > really calling XRSTORS on otherwise uninitialized xsave buffers? Right now if we do fpstate_init(), without this patch, it will trigger a warning from copy_kernel_to_fxregs() when the task is scheduled.
